1. Field of the Invention
The present invention relates to an automatic chemical analysis system for obtaining an amount of a specific component of, for example, a sample material in chemical and biochemical fields, and more particularly, to a stirring apparatus utilized for the automatic chemical analysis system for stirring liquid sample material and reagent.
2. Discussion of the Background
An automatic chemical analysis system is a system in which a liquid sample material, called merely the sample hereinbelow, and a reagent, each of a predetermined amount, are supplied in a reaction vessel in which the sample and the reagent are stirred to mix them together as a sample solution or reaction solution. The process of a chemical reaction due to this stirring is measured by means of, for example, an optical measuring device, through detection of change of an absorbance to thereby obtain an amount of a specific component in the sample.
Such an automatic chemical analysis system is provided with a stirring apparatus for stirring and mixing the sample and the reagent together to homogenize its reaction solution, and such stirring is an important process for reproducibility of the reaction. The stirring apparatus generally comprises a stirring member for stirring the sample and the reagent in the reaction vessel, a support mechanism for holding the stirring member, a washing and/or cleaning mechanism for washing the stirring member with a washing water to remove the sample and reagent adhering to the surface of the stirring member and a mechanism for moving the stirring member support mechanism between the washing mechanism and the reaction vessel. In the chemical analysis system, the movement of the stirring member to the reaction vessel, the stirring operation, the movement thereof to the washing mechanism and the washing operation are repeated for the process carried out by the stirring apparatus.
In one example of a known type of stirring apparatus, a screw type stirring member or a plate-like stirring member, which is driven by an electric motor for stirring, is utilized. In another example of a known type stirring apparatus, a bimorf type piezoelectric vibrator formed by bonding piezoelectric elements to both sides of a thin metal plate is utilized as an example which is not driven by an electric motor (for example, as disclosed in U.S. Pat. No. 4,612,291). In this known type of apparatus, a stirring plate or rod formed of a rigid material such as stainless steel is attached to the thin metal plate, and when an A.C voltage is applied thereto, the vibration of the piezoelectric vibrator is transferred to the stirring plate, thus stirring the sample solution.
However, the known stirring member driven by the motor in one of the above examples has less stirring ability in the vertical direction in the reaction vessel, so that the stirring of the sample solution is not sufficiently carried out in the bottom portion and an upper portion of the reaction vessel and involves relatively a great amount of time for the stirring. In order to obviate these defects, when the motor is forcibly driven to increase its revolution, bubbling is caused or air bubbles are involved, and hence, there may occur cases where the sample solution overflows or is splashed from the reaction vessel.
On the other hand, in the known stirring mechanism of another example utilizing the piezoelectric vibrator, in a certain case, the stirring plate is positioned so that the width direction of the stirring plate attached to the front end of the piezoelectric vibrator has an angle, for example 90.degree., with respect to the moving direction of the stirring plate (tangential direction in a case of arcuate movement). In such case, since the vibrating direction, i.e. thickness direction normal to the width direction, and the moving direction of the agitating plate are in accord with each other, the stirring plate may be greatly vibrated due to an inertia force, for example. Particularly, this vibration will be remarkable when the stirring plate is continuously moved in horizontal and vertical directions. For this reason, for example, when the stirring plate is lowered into the reaction vessel for stirring, there is a fear of colliding of the stirring plate with the edge portion of the reaction vessel, resulting in breakage or bending thereof in an adverse case, and moreover, the reaction solution adhering to the stirring plate and the washing liquid may be splashed due to such vibration during the movement of the stirring plate.
Furthermore, at the time of washing the stirring plate, the washing liquid adheres to the surface of the stirring plate, but in the described known example, the washed stirring plate is utilized as it is for the next stirring, so that there is a fear of diluting the sample solution and hence obtaining inaccurate data, thus being inconvenient.